Patch antennas are generally well known in the art and generally consist of a metal or conductive patch suspended over a ground plane. The assembly is usually contained in a plastic radome, which protects the structure from damage. Similar to patch antennas, microstrip antennas generally provide a similar configuration constructed on a dielectric substrate, usually employing the same sort of lithographic patterning used to fabricate printed circuit boards. Since both types of antennas share similar features and rely on similar operational principles, the following description will refer mainly to patch antennas, with the understanding that a person of skill in the art could equally apply the principles and concepts discussed herein to the fabrication of a microstrip antenna.
Each patch antenna will generally comprise a radiating patch suspended or otherwise disposed over a larger ground plane, with one or more feed mechanisms provided to operate the antenna. Common radiating patch shapes are square, rectangular, circular and elliptical, but other continuous shapes are generally possible. Because such antennas have a very low profile, are mechanically rugged and can be conformable, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio frequency (RF) communication devices and systems, for example mounted at base stations or the like.
Patch antennas are also relatively inexpensive to manufacture and design because of their comparatively simple two-dimensional physical geometry. In many cases, an array of patches can be manufactured and/or mounted in a combined fashion to provide greater operating performance (e.g. higher gain, beam shaping, etc.). For example, an array of patches can be printed on a single substrate using lithographic techniques, or the like, which can provide much higher performances than a single patch at little additional cost.
An advantage inherent to patch antennas is the ability to have polarization diversity. For example, a patch antenna can be designed to have Vertical, Horizontal, Right Hand Circular (RHCP) or Left Hand Circular (LHCP) Polarizations, using multiple feed points, or a single feed point with asymmetric patch structures, for example. This property allows patch antennas to be used in many types of communication links that may have varied requirements. For instance, in a beamformed or steerable antenna system, such as may be used in base stations for cellular telephone networks, an antenna may be comprised of an array of identical antenna elements and a dual feed network enabling the dual feeding of each patch element to emanate a radiation pattern comprising orthogonally polarized beams. Therefore, care should be taken to design a patch element that provides satisfactory performance while satisfying the various design criteria of the radiating element. In one such example, the two polarizations are set at +/−45°, as provided by a square patch radiator oriented along a diagonal relative to the array.
As introduced above, different feed mechanisms have been developed to operate patch antennas; examples of such feed mechanism include, for instance, patch edge feeding mechanisms, probe feeding mechanisms, aperture-coupling feeding mechanisms, capacitive feeding mechanisms and the like. In particular, due to its wide bandwidth nature, capacitive feed mechanisms have been of particular interest. In general, as described in the below-cited articles, traditional capacitive feed mechanisms involve the capacitive coupling of the radiating patch (resonator) with a feeding pad or element disposed in a coplanar fashion at a selected distance away from the patch. In dual capacitive feeding, one such feeding pad is generally provided for each polarization. While this configuration may provide some advantages in the fabrication of such antennas (i.e., simple structure and single layer combination), various drawbacks present themselves, particularly, in wideband planar array applications. Such drawbacks may include, but are not limited to, poor return loss (RL), narrow bandwidth (BW), low isolation (ISO) between two dual polarizations, low cross polarization discrimination (XPD) within the antenna element, and poor mutual coupling (MC) between antenna elements.
Different solutions have been proposed to overcome at least some of these drawbacks, as described in the following articles: A Broadband Microstrip Antenna by J. S. Roy, Microwave and Optical Technology Letters (Vol. 19, No. 4); Single Layer Capacitive Feed for Wideband Probe-Fed Microstrip Antenna Elements by G. Mayhew-Ridgers et al., IEEE Transactions on Antennas and Propagation (Vol. 51, No. 6); Efficient Full Wave Modeling of Patch Antenna Arrays with new Single-Layer Capacitive Feed Probes by G. Mayhew-Ridgers et al., IEEE Transactions on Antennas and Propagation (Vol. 53, No. 10); Wideband Quarter-Wave Patch Antenna with a Single-Layer Capacitive Feed on a Finite Ground Plane by J. Joubert et al., Microwave and Optical Technology Letters (Vol. 45, No. 3); Probe Compensation in Thick Microstrip Patches by S. Hall, Electronic Letters (Vol. 23 No.11); and Single Patch Broadband Circularly Polarized Microstrip Antennas by Kin-Lu et al., (IEEE-APS symposium 2000).
While some performance improvements may be observed using these solutions, relatively poor ISO and XPD within the antenna element, and poor MC between array elements, for example in the context of a planar bi-sector array but also in other applications, as will be appreciated by the person of skill in the art, generally yield high side lobe levels and low gains, and so cannot be used in a real system because of system capacity and coverage limitations.
Therefore there is a need for a new patch antenna, element thereof and feeding method therefor that overcome some of the drawbacks of known technology, or alternatively, provides the public with a new and useful alternative to such technology.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the invention.